The present invention relates generally to an apparatus and method for selectively delivering an ion stream and, more particularly, to such an apparatus and method for controlling uniformity between element output in a multi-element iongraphic print head.
In ionographic devices such as those described in U.S. Pat. No. 4,524,371 to Sheridon et al., or U.S. Pat. No. 4,463,363 to Gundlach et al., an ion producing device generates ions to be directed past modulation electrodes to an imaging surface in imagewise configuration. In one type of ionographic device, ions are produced at a coronode supported within an ion chamber, and a moving fluid stream carries the ions out of the chamber. At the chamber exit, a plurality of modulation electrodes are modulated with a control voltage to selectively control passage of ions through the chamber exit. Ions directed through the chamber exit are deposited on a charge retentive surface in imagewise configuration to form an electrostatic latent image developable by electrostatographic techniques for subsequent transfer to a final substrate, such as a sheet of paper. The arrangement produces a high resolution, non-contact printing system. Other types of ionographic devices exist that operate similarly, but do not rely on a moving fluid stream to carry ions to a surface.
Although the device may be fabricated with a high quality process, there is typically a measurable nonuniformity among the ion outputs associated with each modulation electrode. Part of the nonuniformity may be caused by variations in the chamber exit width and air flow velocity along the length of the chamber exit. Further, because the typical width of the chamber exit is only three to six one-thousandth of an inch, contaminants typically found in room air, such as organics and combustion byproducts can be deposited at particular portions of the exit, reducing ion flow through one or more physical mechanisms.
Publications of general interest include U.S. Pat. No. 4,467,333 issued to Seimiya et al., which discloses an ion control electrode and a common electrode arranged to face each other through an insulating layer; U.S. Pat. No. 3,473,074 to Joannou, which discloses a print-drum confronted by an array of "mosaic" ground electrodes; U.S. Pat. No. 3,673,598 to Simm et al., which discloses image-wise controlled charging of an insulating recording material; and U.S. Pat. No. 4,435,066 to Tarumi et al., which discloses a common electrode and an optional ion flow condenser electrode.